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Date:      Thu, 17 Jan 2002 09:52:52 +0200
From:      "Toomas Aas" <toomas.aas@raad.tartu.ee>
To:        "Timothy Radigan" <rad2921@cup.edu>, freebsd-questions@freebsd.org
Subject:   Re: Console Error Messages
Message-ID:  <200201170753.g0H7rYr19586@lv.raad.tartu.ee>
In-Reply-To: <004601c19ecc$095b4d20$9601a8c0@newrevolutions.net>

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Hi Timothy!

On 16 Jan 02 at 15:26 you wrote:

> dc0: TX underrun -- increasing TX threshold

Ethernet cards nowadays send out frames in such a way that they 
start transmitting before they have received the entire packet from 
the system. The card knows of a parameter called 'TX threshold', 
which specifies the number of octets that the card must have at 
hand to start transmitting the frame.

For instance, if TX threshold is 64 octets and a frame of 1500 
octets is being sent, the adapter starts transmitting as soon as it 
has received the first 64 octets and hopes to receive the rest of 
the data from the upper layers in the stack while transmitting 
what it already has. If the processing in the upper layers is not 
as fast as expected, the ethernet controller gets in trouble. It 
has already sent out a part of the frame but suddenly it notices 
that the rest of the data is not there! This is the 'TX underrun' 
error.

The dc driver is apparently smart enough to notice such error and 
dynamically increase the TX threshold value, hoping to avoid such 
unfortunate events in the future. Thus the 'increasing TX 
threshold' message.

It would be good idea to specify the TX threshold as 1514 octets 
from the very beginning, to avoid sending garbage (partial frames) 
to the wire at all. I have no idea if dc driver allows to specify 
TX threshold value on command line.

> Other error messages I get are from named and dhcpd.

Sorry, I hope someone else can help you here. My knowledge on named 
and dhcpd is shallow enough.

--
Toomas Aas | toomas.aas@raad.tartu.ee | http://www.raad.tartu.ee/~toomas/
* I`m not as think as you drunk I am...


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